Generally, while a vehicle is driving or stopped, wheels contacting the ground rotate by the rotation of a steering wheel. That is, when a steering wheel is rotated in the left or right direction, wheels are rotated in the same direction. However, because wheels are in contact with the ground, there is a problem with a difference in an amount of rotation between the steering wheel and the wheels due to a friction force occurring between the wheels and the ground.
To solve the problem, a torque sensor is provided to measure and correct a difference in rotation angle between the steering wheel and the wheels. The torque sensor measures a difference in rotation angle between the steering wheel and the wheels, and allows the wheels to further rotate as much as the measured difference using a separate driving means, to steer the vehicle in an intended direction safely and precisely, thereby increasing steering convenience.
The torque sensor is largely classified into a contact type and a non-contact type, and due to noise and durability reduction problems of the contact type, non-contact torque sensors are being recently employed. Non-contact torque sensors are largely classified into magnetoresistive, magnetostrictive, capacitive and optical detection techniques.
A traditional magnetoresistive detection-based torque sensor provide in an electric assisted steering system is constructed such that a steering wheel manipulated by a driver is connected to the top of an input axis, and the bottom of the input axis is connected to the top of an output axis by a torsion bar. Also, the bottom of the output axis is connected to the wheels, and the outside of the bottom of the input axis including the torsion bar and the top of the output axis is protected by a housing. Inside the housing, the torque sensor and the driving means as described above are provided. Representatively, Korean Patent Publication No. 10-2007-0043000 and U.S. Pat. No. 8,327,722 are taken as examples. However, these traditional torque sensors have many components, are complex, and suffer from a number of losses during magnetic induction.